A balun circuit typically takes the form of a three-port passive device that may be used to connect balanced circuits (e.g., an antenna) to unbalanced circuits. For example, the balun circuit may provide a connection between one unbalanced transmission line and two balanced transmission lines. In such an example, the balun circuit may be designed such that the balanced transmission lines output signals that are equal in magnitude but with a phase difference of 180 degrees.
One type of balun circuit for transmission of microwave signals uses a microstrip-to-slotline transition. This transition generally includes a single input stripline and single output stripline coupled to one another via a slotline. Conventional microstrip-to-slotline transition balun circuits are subject to bandwidth and frequency constraints. As such, there is a need for a ultra-wideband microstrip-to-slotline transition balun circuit. Such circuits may desirably work at frequencies greater than 11 GHz, greater than 45 GHz, or up to and beyond 110, and even 200 GHz.